The present invention relates a wiring forming method for a semiconductor device and a semiconductor device of forming wirings made of a metal material in connection holes or wiring grooves formed on a semiconductor substrate for conducting connections between wirings and semiconductor substrates and, more in particular, it enables complete and uniform filling of the metal material into connection holes or wiring grooves without complicating a production process.
Wirings in integrated circuits such as LSIs have been generally formed by fabricating films of aluminum (Al) series alloys deposited by a sputtering method by using, for example, photolithography or dry etching.
However, along with increasing degree of integration in semiconductor integrated circuits, diameters for connection holes or diameters for wiring grooves apertured for conducting connection between wirings and semiconductor substrates have become finer and an aspect ratio of them has been increased more and more. Therefore, it is difficult to form wirings at a predetermined thickness as far as the inside of the connection holes by the sputtering method to result in a problem of lowering the step coverage, increasing the resistance of contact hole wirings and deteriorating electro-migration durability.
In order to avoid them, a method of forming wirings to a vertical wiring portion in connection holes by a CVD method (chemical vapor deposition method) using tungsten (W) is adopted in LSIs under a design rule below half-micron.
However, in the existent method of forming wirings by the CVD method using tungsten, since the resistance of tungsten is high, it is necessary to leave a tungsten film formed on the entire surface of a substrate only in the connection holes while removing other portions by a dry etching method or chemical and mechanical polishing method (CMP) and form wirings of an aluminum series alloy again. Therefore, this gives rise to a problem of making the wiring forming step lengthy to increase the cost.
On the other hand, as the size for the wirings has become finer, it has been desired for wiring materials of high electro-migration durability and low resistance, and a film deposition method and a wiring fabrication method have now been under study for using copper capable of satisfying such a demand for the wiring material.
However, since a film of copper can not be deposited uniformly in a connection hole by a usual sputtering method, a method of depositing the copper film by a CVD method has been studied, but it still leaves a subject such as for the development of organic metal compounds of copper as a starting material and the development for CVD apparatus.
Further, while an electrolytic plating method for copper has also been studied, electrodeposition proceeds at the periphery outside of the fine connection holes or wiring grooves to at first close inlets for the connection holes or wiring grooves, which causes a problem of difficulty for filing copper in the fine connection holes without forming voids.
Further, it is difficult to fabricate copper by dry etching and it has been proposed, for example, a DUALDER machine method of forming contact holes and wiring grooves to an insulation film, depositing copper for the entire surface and then removing excess copper by a chemical and mechanical polishing method thereby properly forming wirings having vertical connection portions. Development for the technique of properly filling and depositing a copper film into hole or groove portions of high aspect ratio such as connection hole or wiring grooves has also been desired with an aim of applying to this method.
In view of the above, the present invention has been accomplished taking notice of the foregoing not yet solved subject and it is an object thereof to provide a selective plating method capable of completely, and uniformly filling groove or hole portions of high aspect ratio and a wiring forming method for a semiconductor device using the same, as well as a semiconductor device using the method.
In order to attain the foregoing object, the present invention provides a method of forming wirings for a semiconductor device, which comprises the steps of forming concaved wiring channels in an insulation film deposited on a semiconductor substrate, forming a first conductor layer having a first deposition overvoltage as a deposition overvoltage required for depositing a copper series metal material in a plating solution at a predetermined rate to the surface of the insulation film including the inner surface of the concaved portion of the wiring channels, then forming thereon a second conductor layer having a second deposition overvoltage higher than the first deposition overvoltage as the deposition overvoltage so as to cover a region except for the inner surface of the concaved portion of the wiring channels, subsequently, dipping at least the inner surface of the concaved portion of the wiring channels into the plating solution and applying a plating treatment at a deposition overvoltage higher than the first deposition overvoltage and lower than the second deposition overvoltage to deposit the copper series metal material, and polishing the deposited metal material thereby forming wirings.
That is, the first conductor layer having the first deposition overvoltage as the deposition overvoltage is formed to a region including the inner surface of the concaved portion of the wiring channels such as connection holes or wiring grooves formed in the concaved shape to the insulation film deposited on the semiconductor substrate, for example, by a CVD method, and then the second conductor layer having the second deposition overvoltage as the deposition overvoltage is formed there on so as to cover the surface of the insulation film except for the inner surface of the concaved portion of the wiring channels, for example, by a sputtering method. Then, they are dipped in the plating solution such that at least the entire surface of the inner surface of the concaved portion of the wiring channels is dipped in the plating solution, and plating is applied at a deposition overvoltage higher than the first deposition overvoltage and lower than the second deposition overvoltage. Since the deposition overvoltage is a voltage required for depositing the copper series metal material in the plating solution at a predetermined rate, the metal material is not deposited on a portion in which the second conductor layer is exposed, whereas chemical reactions are taken place between the metal material in the plating solution and the first conductor layer to deposit the metal material and apply copper plating to the portion in which the first conductor layer is exposed. That is, since copper plating is applied only to the portion in which the first conductor layer is exposed, namely, only to the inside of the concaved portion of the wiring channels intended to be applied with plating, to result in a copper-filled state, a wiring consisting of copper filled in the wiring channels can be obtained by polishing the copper.
In this case, the second conductor layer is preferably formed by a highly anisotropic deposition method. This is done for forming the second conductor layer to a region except for a region to be plated, namely, only to a region except for the wiring channels and the formation of the second conductor layer to the wiring channels can be avoided.
Further, it is preferred that each wiring channel has an aspect ratio of 1 or greater and 5 or less and a width of 1.0 xcexcm or less. This is so defined for avoiding the formation of the second conductor layer at the bottom of the wiring channels upon forming the second conductor layer, for example, by a sputtering method.
Further, in a case of applying to a semiconductor device of a multi-layered wiring structure, plating is applied to form wirings and then wirings are conducted by forming a metal film further thereon. When wirings are formed on an insulator, a thin electrically conductive film is generally put between them with an aim, for example, of improving adhesion and electro-migration durability. In this case, since the first semiconductor substrate, the step of forming wirings can be shortened by utilizing the layer as the thin electrically conductive film.
Further, the deposited metal material is preferably polished by a chemical and mechanical polishing method by which the wirings can be formed easily and accurately.
Further, when making the first conductor layer with titanium nitride, the second conductor layer with titanium and the metal material with the copper series metal material, copper wirings uniformly filled in the concaved portion of the wiring channels can be formed by forming a titanium nitride film to a region including the inner surface of the concaved portion of the wiring channels such as connection holes or wiring grooves, forming a titanium film so as to cover the surface of the insulation film except for the wiring channels and then dipping them into a plating solution.
Further, the present invention provides a semiconductor device comprising a first conductor layer formed to the surface of an insulation film including the inner surface of a concaved portion of concaved wiring channels formed in the insulation film on a semiconductor substrate and having a first deposition overvoltage as a deposition overvoltage required for depositing a copper series metal material in a plating solution at a predetermined rate, a second conductor layer formed thereon after the formation of the first conductor layer so as to cover a region except for the inner surface of the concaved portion of the wiring channels and having a second deposition overvoltage higher than the first deposition overvoltage as the deposition overvoltage, and wirings formed by dipping a portion at least including the first conductor layer in the plating solution, applying a plating treatment at a deposition overvoltage higher than the first deposition overvoltage and lower than the second deposition overvoltage and polishing the copper series metal material deposited on the inner surface of the concaved portion in which the first conductor layer is exposed by a chemical and mechanical polishing method.
That is, a first conductor layer having the first deposition overvoltage as the deposition overvoltage is formed on the surface of the insulation film including the inner surface of the concaved portion of the wiring channels such as the connection holes or the wiring grooves formed in the insulation film on the semiconductor substrate and, after the formation of the first conductor layer the second conductor layer having the second deposition overvoltage as the deposition overvoltage is formed thereon so as to cover the region except for the inner surface of the concaved portion of the wiring channels. Further, the first conductor layer not covered with the second conductor layer is formed with a film of the metal material, that is, copper deposited by applying a plating treatment at a deposition overvoltage higher than the first deposition overvoltage and lower than the second deposition overvoltage in a state of dipping the inner surface of the concaved portion of the wiring channels in the plating solution and the metal film is polished by the chemical and mechanical polishing method to form the wirings. That is, wirings are formed in a state of filling copper only in the wiring channels. Since the wirings made of copper are formed by applying copper plating, copper for the wirings can be filled uniformly to obtain wirings of high performance even if the size of wiring channels is fine.
When making the first conductor layer with titanium nitride, the second conductor with titanium and the metal material with the copper series metal material, copper wirings filled uniformly in the concaved portion of the wiring channels can be obtained by forming a titanium nitride film to a region including the inner surface of the concaved portion of the wiring channels such as connection holes or wiring grooves, forming a titanium film so as to cover the surface of the insulation film except for the wiring channels and then dipping them in a plating solution.
Further, the present invention provides a selective plating method, which comprises the steps of forming a first conductor layer having a first deposition overvoltage as a deposition overvoltage required for depositing a metal material in a plating solution at a predetermined rate to a portion including a plating region to be plated in the surface of a material to be plated, then forming thereon a second conductor layer having a second deposition overvoltage higher than the first deposition overvoltage as the required deposition overvoltage so as to cover a region except for the plating region, subsequently, and dipping the material to be plated into the plating solution and applying a plating treatment at a deposition overvoltage higher than the first deposition overvoltage and lower than the second deposition overvoltage.
That is, the first conductor layer having the first deposition overvoltage as the deposition overvoltage is formed on the surface of the material to be plated including the plating region for applying plating, and the second conductor layer having the second deposition overvoltage higher than the first deposition overvoltage as the deposition overvoltage is then formed thereon so as to cover the region except for the plating region. That is, since the second conductor layer is formed so as to cover the region not applied with plating, the second conductor layer is formed also in a case where the first conductor layer is formed in the not plated region, so as to cover the first conductor layer in such a region. Therefore, the first conductor layer is exposed only in the plating region. Then, the material to be plated is dipped in the plating solution and applied with the plating treatment at a deposition overvoltage higher than the first deposition overvoltage and the lower than the second deposition overvoltage. That is, in a case of electrolytic plating, for example, an electrode voltage higher than the first deposition overvoltage and lower than the second deposition overvoltage is set between the underlying metal to be applied with plating, that is, the first conductor layer in this case and the counter-electrode and, in a case of electroless plating, the oxidation reduction potential of an oxidant is set such that it is higher than the first deposition overvoltage and lower than the second deposition overvoltage.
In this case, since the deposition overvoltage is a voltage required for depositing the metal material in the plating solution at a predetermined rate, plating is not applied to the portion in which the second conductor layer is exposed since the plating treatment is conducted at a voltage lower than the second deposition overvoltage and no chemical reaction is taken place. On the other hand, chemical reaction is taken place between the first conductor layer and the metal material in the plating solution at a portion in which the first conductor layer is exposed, to form a film of electrolysis products in a case of the electrolytic plating and of deposition products by oxidizing reaction between the metal material and a reducing agent in a case of the electroless plating, and plating is applied by the metal material in the plating solution. Therefore, plating is applied only to the region in which the first conductor layer is exposed, namely, plating is applied only to the plating region.
When the first conductor layer is formed to the region at least including the inner surface of the concaved portion and the second conductor layer is formed so as to cover the region except for the inner surface of the concaved portion, the first conductor layer having the first deposition overvoltage as the deposition overvoltage is formed at least in the region including the inner surface of the concaved portion and the second conductor layer having the second deposition overvoltage as the deposition overvoltage is formed so as to cover the region except for the inner surface of the concaved portion. Accordingly, plating is applied only to the region in which the first conductor layer is exposed, that is, only to the inner surface of the concaved portion by dipping the material to be plated in the plating solution and applying plating at a deposition overvoltage higher than the first deposition overvoltage and lower than the second deposition overvoltage. Since a metal film of an optional thickness can be obtained depending on the dipping time, a metal film with no voids and of uniform thickness filled in the concaved portion can be obtained, for example, also in a case of a fine concaved portion.
Further, when making the first conductor layer with titanium nitride, the second conductor layer with titanium and the metal material with the copper series metal material, a uniform copper metal film can be formed easily only to the region in which the titanium nitride is exposed, for example, by forming a titanium nitride film at least including a region intended to be formed with a copper metal film and, forming a titanium film so as to cover other region than the above and then dipping them into the plating solution.